Two modes are supported in the prior 3GPP E-UTRA system: frequency division duplex (FDD) and time division duplex (TDD). In TDD mode, the length of each radio frame is 10 ms and is composed by two 5 ms length half-frames. Each half-frame is composed by eight 0.5 ms timeslots and three special fields, namely, downlink pilot timeslot (DwPTS), guard period (GP) and uplink pilot timeslot (UpPTS). Two timeslots form a sub-frame, and the DwPTS, GP, and UpPTS form a special sub-frame. The length of a sub-frame is 1 ms.
Currently, two modes are available to feed back an acknowledgment or negative acknowledgment (ACK/NAK) of multiple downlink sub-frames in an uplink sub-frame in the 3GPP E-UTRA system: multiplexing and bundling. In multiplexing mode, if the ACK/NAK is fed back in a physical uplink control channel (PUCCH), the feedback is related to the uplink-downlink configuration; if the ACK/NAK is fed back in a physical downlink shared channel (PDSCH), the number of bits fed back depends on whether an uplink grant (UL Grant) signaling exists. If the UL Grant signaling exists, the number of bits that the user equipment (UE) is required to feed back is specified through an uplink data assignment indicator (UL DAI) field in the signaling. If a base station (BS) schedules x of the total N downlink sub-frames, the UE feeds back x ACKs/NAKs; if no UL Grant signaling exists, the UE feeds back N bits and a NAK to those non-scheduled downlink sub-frames.
In bundling mode, only 1-bit ACK/NAK information is fed back, in the PUCCH or in the PUSCH, to indicate the details of all the scheduled downlink sub-frames. So long as the feedback to a scheduled downlink sub-frame is a NAK, the final feedback is a NAK. The final feedback is an ACK only when feedbacks to all the scheduled downlink sub-frames are ACKs.
Two data scheduling modes are defined in the current Long Term Evolution (LTE) protocol: dynamic scheduling and semi-persistent scheduling (SPS). In dynamic scheduling mode, each new data packet has a control signaling—physical downlink control channel (PDCCH) to indicate resources and transmission mode. The UE receives downlink data and transmits uplink data according to the PDCCH delivered by the BS. In SPS mode, the BS sends a PDCCH control signaling only when the SPS transmission is activated. The UE activates the SPS transmission according to the position and time indicated by the PDCCH. The UE transmits and receives new data packets in a certain period until another PDCCH in a special format terminates the SPS transmission.
Because the PDCCH is used for notification in both dynamic scheduling and semi-persistent scheduling modes, the UE differentiates whether the scheduling mode is dynamic scheduling or semi-persistent scheduling by different scrambled IDs in a cyclic redundancy check (CRC) of the PDCCH. In dynamic scheduling mode, the CRC of the PDCCH is scrambled with a cell radio network temporary identifier (C-RNTI); in semi-persistent scheduling mode, the CRC of the PDCCH is scrambled with an SPS-C-RNTI. When the UE detects the PDCCH scrambled with the SPS-C-RNTI, the UE activates the semi-persistent transmission, and receives or transmits data according to the indication in the PDCCH. Within the subsequent period of time, the UE receives and transmits data only according to the position indicated by the PDCCH when the semi-persistent transmission is activated for the first time, making it unnecessary to notify the UE of the position of SPS data packet resources through the PDCCH each time. When the position of SPS resources needs to be changed, a new PDCCH may be used to replace the previous semi-persistent scheduling configuration until the semi-persistent transmission is cancelled by a PDCCH scrambled with an SPS-C-RNTI in a special format when the period of SPS data expires.
However, in uplink ACK/NAK multiplexing mode in the prior art, the first position of K ACKs/NAKs fed back by the UE is the ACK/NAK of the SPS sub-frame, and the position of the UL ACK/NAK of other sub-frames is arranged in the sequence of a downlink data assignment indicator (DL DAI). If the UE does not detect any data in the sub-frames, the UE feeds back a NAK. When the UE loses the SPS activation signaling, the UE feeds back a NAK at the first position. Based on the NAK, the BS thinks that the control signaling is received properly but data is wrong, thus receiving incorrect ACK information. As a result, the BS does not retransmit a PDCCH, and the UE still does not know the position of the semi-persistent transmission, which causes unnecessary retransmission.